Chemicals, radiation, and copying and repairing errors can cause chromosomal DNA-sequence damage {mutation}|. People can inherit changed genotypes.
types
Single nucleotides, short regions, genes, and chromosomes {muton} can mutate. Mutations include nucleotide deletions, insertions, and changes {point mutation}. Mutations include chromosome number or structure changes. DNA regions can delete, insert, invert, double, and alter.
rate
Trait mutation rate is 10^-4 to 10^-6 per generation. One to ten percent of cells have mutations.
affects
Mutations are typically bad, but bad mutations can be good in new environments. Mutations degrade good, working genetic code to make it more variable, and this process adds to genetic variability. Higher mutation rates affect organisms with more genes more.
experiments
In animals or plants, to discover if genes {candidate gene} relate to diseases, researchers mutate genes to see if mutation causes disease symptoms.
Higher mutation rates typically cause poorer adaptation {error catastrophe, mutation}.
Modified plant genes can go only to ovules {maternal inheritance}, not to pollen.
Codons, with same first two bases but different third base, can code for the same amino acid. For those codons, third-base mutations {silent mutation} do not make any difference to survival.
However, different codons bind to different t-RNAs, and some t-RNAs are more abundant than others. Times to bind scarcer t-RNA are longer than times for more abundant t-RNA. Time differences can affect protein folding, change protein structure, and affect function.
Silent mutations can accumulate and eventually encode new proteins. For example, mutations can cause body-part replication. Subsequent generations can modify replicated parts to make new structures and functions.
Gene changes can help identify which genes are performing which functions.
process
Plasmids and other vectors can have genes. Added chemicals or enzymes can mutate genes {in vitro mutagenesis}. Vectors go into hosts, express genes, and make protein.
methods
Gene changes can be at restriction endonuclease sites. If sites have overhanging strands, S1 nuclease can remove overhanging single-strand DNA, or DNA polymerase can extend shorter strands, to make blunt ends. Linkers can attach to blunt ends.
Chemicals can alter gene nucleotides. Sodium bisulfite makes C into U. Hydrazine and formic acid delete nucleotide nitrogenous base, leaving sugar and phosphate. At low nucleotide concentrations or in harsh chemical conditions, DNA polymerase can add wrong nucleotides during DNA synthesis.
In vitro mutagenesis {site-directed mutagenesis} can study binding sites and functional regions. Site-directed mutagenesis hybridizes synthetic 10-base to 15-base oligonucleotides to DNA sites. Oligonucleotides differ from original sequences by one nucleotide at end. Oligonucleotides hybridize well to original sequences, because they differ by only one nucleotide. Hybridized sequences replicate to make mutated genes.
enzymes
DNA ligase connects perfectly aligned DNA strands. Mutated ends do not ligate {ligase-mediated}, showing mutation locations. RNase A cuts DNA-RNA complexes where sequences mismatch and can detect mutation locations. Osmium tetroxide and hydroxlamine cut at unmatched C or T bases. Restriction enzymes fragment single-strand DNA. Different DNA fragments have different conformations and so different mobilities {single-stranded conformation polymorphism} (SSCP).
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Date Modified: 2022.0225